A variety of diseases exist that require regular treatment by injection of a medicament. Such injections can be performed by using injection devices, which are applied either by medical personnel or by patients themselves. As an example, type-1 and type-2 diabetes can be treated by patients themselves by injection of insulin doses, for example once or several times per day. For instance, a pre-filled disposable insulin pen can be used as an injection device. Alternatively, a re-usable pen may be used. A re-usable pen allows replacement of an empty medicament cartridge by a new one. Either pen may come with a set of one-way needles that are replaced before each use. The insulin dose to be injected can then for instance be manually selected at the insulin pen by turning a dosage dial and observing the actual dose from a dosage window of the insulin pen. The dose is then injected by inserting the needle into a suited skin portion and pressing an injection button of the insulin pen. To be able to monitor insulin injection, for instance to prevent false handling of the insulin pen or to keep track of the doses already applied or remaining, it is desirable to measure information related to a condition and/or use of the injection device, such as for instance information on the injected insulin type and dose.
For a good treatment of insulin it is necessary to keep a diary to document the day, time and amount of insulin dose. Some patients forget to write the information down or cannot remember when and how much insulin they have injected. Therefore, there is a strong need for further support or automation of this process to make it easier for the patient to keep track of his/her diary.